In the background behind the German front line the slopes of the famous Aubers Ridge, the barrier that blocked the road to Lille, rose steadily to a height of more than fifty metres, almost a mountain-range in this flat country, giving the enemy a very fine view of all our activities. Passing Billet and Ration Farms, which bristled with R.E. material and salvage, we crossed a duck-board bridge and struck the subsidiary line of the Bois Grenier sector on the immediate right of the Rue du Bois. We plodded steadily along the duck-board track till Desolanque Farm (or Deplanque Farm, as its real name is: the official map is wrong), the usual ruin surrounded by a rectangular moat, appeared in view. The subsidiary line ran about fifty yards in front of this, and close up against it, in a long concrete dug-out, were the Battalion Headquarters that we were seeking. Down the steps into this dug-out we descended with more haste than dignity, as the enemy selected this particular moment to send a shower of "whizz-bangs" into the farm, just skimming the top of the dug-out. In the narrow stairway we met the Commanding Officer, full of wrath. "Whizz-bangs" generally meant that too many people were wandering about in the vicinity of the farm, and strict orders had been issued to prevent this. It is extraordinary how insensible to danger the average man soon becomes, and the most reasonable orders for the protection of life are ignored or disregarded unless very strictly enforced. The Headquarters consisted of a very long concrete passage with five small rooms opening on to it--the mess, two sleeping rooms, a signal office, and the Adjutant's office and sleeping room combined. All the rooms were small and required artificial light, and a general feeling of chilly damp prevailed everywhere. We arranged ourselves as best we could in the mess; but we were all crowded together in a space far too small for the number of occupants, and the table was covered with maps, defence schemes, aeroplane photographs, and the usual litter of a trench headquarters, not to mention box respirators, tin helmets, and other impedimenta which are hastily doffed on entering a dug-out. [Illustration: RUE DE BOIS SECTOR.]